This project involves intracellular recordings from photoreceptor cells in an in vitro preparation of mammalian retina. An arterially perfused eyecup preparation from the eastern gray squirrel, Sciurus carolinensis, has been developed in this laboratory for this purpose. We have recently begun to study the response characteristics of cells which are located in the distal layers of this retina and which produce hyperpolarizing reponses to stimulation with light. It is anticipated that cells of this type will include horizontal cells as well as photoreceptor cells. Since horizontal cells are known to affect the response characteristics of photoreceptors, an investigation of these units will also be included in this project. We will study the spectral sensitivities, intensity-response characteristics, flash sensitivities, response time courses, and receptive field properties of these units. We are particularly interested in studying the nature and extent of interactions between photoreceptors, and between photoreceptors and horizontal cells. In addition we propose to correlate the physiology and morphology of these units by injecting studied cells with Procion yellow, Lucifer yellow, or horseradish peroxidase and studying appropriate morphological characteristics.